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ETJOURNAL oFENGINEERING &TECHNOLOGY Autumn 2010 co N co LO , 0) N N N Z (f) (f) Enhancing Thermal Efficiency of Steam Turbine In Coal Fired Thermal Power Plant Sanjeev Sharma' R. J. Lalwanj2 Introduction Abstract Thispaper describes some options for conservation of energy in the turbine section of a 210MW unit of a coal fired thermal power plant. It shows the need and importance ofenergy conservation. Inthispaper, data is collected from the power plant and analyzed for determining different performance parameters of the turbinesection. Acontinuing concern ofoperators ofsteam turbines is increasing operating costs. These costs reflect not only the rising cost of fuel and material but also the decreased efficiency of the aging turbine fleet. Over time, damage to turbine components and increased steam leakage are the major factors resulting in lost efficiency Steam leakage alone can account for as much as 80 percent of the efficiency losses in turbines. Since the cost of fuel and materials is largely beyond the control of steam turbine operators, the primary mechanism for realizing savings is in the improvement ofturbine efficiency Due to increasing operating costs, the owners and operators of steam electric generation plants work under considerable pressure to maximize the reliability, efficiency and capacity of their plants. In this regard, the single most critical component of the steam electric generation plant is the steam turbine. Most steam turbines operate below optimum efficiency levels by as much as several percentage points due to many factors including damage, deposits, misalignment, unusual flow phenomena and steam leakage. Additionally, reliability is frequently compromised by these factors. Sub-optimum unit performance is becoming increasingly more costly as prices for fuel and materials rise and production competition becomes tougher. Detailed evaluation of the turbine's operating state, and practical selection of performance improvements are critical to optimum operation of the electric generation plant. Application and implementation of state-of- the- art after-market replacement components, along with improved operating procedures and techniques, can lead to significant improvements in reliable performance and sustained optimum efficiency and capacity. Partly due to rising operating costs, as well as an increasingly competitive energy marketplace, steam turbine thermal performance has become an extremely important aspect of the power industry's fleet maintenance programs. Although returning the turbine to its maximum ••..•..• -r----1 Keywords Coal Fired Thermal Power Plant, Steam Turbine,EnergyConservation, ThermalEfficiency 'Asst. Prof (Mechanical Engineering Department.) Skyline Institute of Engineering & Technology, Greater Noida India 'Dean & HOD (Mechanical Engineering Department.) Skyline Institute of Engineering & Technology, Greater Noida India
Transcript
  • ETJOURNALoFENGINEERING&TECHNOLOGY

    Autumn 2010coNcoLO,0)NNNZ(f)(f)Enhancing Thermal Efficiency

    of Steam Turbine In Coal FiredThermal Power Plant

    Sanjeev Sharma' R. J. Lalwanj2

    IntroductionAbstract

    Thispaper describes some options for conservationof energy in the turbine section of a 210MW unit of acoal fired thermal power plant. It shows the need andimportance of energy conservation. In this paper, datais collected from the power plant and analyzed fordetermining different performance parameters of theturbinesection.

    A continuing concern of operators of steam turbines isincreasing operating costs. These costs reflect notonly the rising cost of fuel and material but also thedecreased efficiency of the aging turbine fleet. Overtime, damage to turbine components and increasedsteam leakage are the major factors resulting in lostefficiency Steam leakage alone can account for asmuch as 80 percent of the efficiency losses inturbines. Since the cost of fuel and materials is largelybeyond the control of steam turbine operators, theprimary mechanism for realizing savings is in theimprovement of turbine efficiency

    Due to increasing operating costs, the owners

    and operators of steam electric generationplants work under considerable pressure tomaximize the reliability, efficiency and capacityof their plants. In this regard, the single mostcritical component of the steam electricgeneration plant is the steam turbine. Moststeam turbines operate below optimumefficiency levels by as much as severalpercentage points due to many factors includingdamage, deposits, misalignment, unusual flowphenomena and steam leakage. Additionally,reliability is frequently compromised by thesefactors. Sub-optimum unit performance isbecoming increasingly more costly as prices forfuel and materials rise and productioncompetition becomes tougher. Detailedevaluation of the turbine's operating state, andpractical selection of performanceimprovements are critical to optimum operationof the electric generation plant. Application andimplementation of state-of- the- art after-marketreplacement components, along with improvedoperating procedures and techniques, can leadto significant improvements in reliableperformance and sustained optimum efficiencyand capacity.

    Partly due to rising operating costs, as well as anincreasingly competitive energy marketplace,steam turbine thermal performance has becomean extremely important aspect of the powerindustry's fleet maintenance programs.Although returning the turbine to its maximum ....-r----1

    Keywords Coal Fired Thermal Power Plant, SteamTurbine,EnergyConservation, ThermalEfficiency

    'Asst. Prof(Mechanical Engineering Department.)Skyline Institute of Engineering& Technology, Greater NoidaIndia

    'Dean & HOD(Mechanical Engineering Department.)Skyline Institute of Engineering& Technology, Greater NoidaIndia

  • r RSHrn

    W

    11 12

    LPTIPTHPT

    7

    6

    achievable efficiency is one primary goal of themaintenance overhaul, the industry's trendtowards an increased Mean - Time - Between-Overhaul (MTBO) demands new methods forsustaining high efficiency levels over longerperiods of operation. With recent de.velopment ofcutting-edge technologies, sustained highefficiency has become a practical goal of turbineOperations and Maintenance teams [6].

    A thorough understanding of actual turbinesefficiency level is important and the authoremphasizes that the nucleus of a turbinemaintenance program should be centeredaround the following inspection and repair/improvement activities:

    Accurate and regular programs ofperformance testing

    Regular analysis of test data for identificationoftrends and "events"

    Appraisal of steam path conditions andquantification of damage mechanisms

    3

    5

    1.Determination of turbine heat rateThe following relations are shown to determine turbineheat rate. Heat flow from turbine stop valve, Q, =

    Autumn 2010

    Expert repair of components to return themto their optimum efficiency and reliabilitystates

    Regular application of available components-reliability and efficiency upgrades

    Quantifiable verification of the results ofmaintenance activities

    Throughout the following pages, the author willidentify specific areas of the turbine steam paththat are critical to thermal performance andreliability, and will describe enhancementswhich can significantly improve both reliabilityand efficiency.

    Methodology

    The methodology presented in this study is fordetermining turbine heat rate. It includes therelations for determining the turbine heat rateand for determining the estimated savings inenergy and its equivalent monetary worth.

  • ETJOURNALoFENGINEERING&TECHNOLOGY

    Autumn 2010

    DATA OBTAINED, OCT.30, 2008 from Ropar Power Plant, Punjab.Table 1 Designed and tested values of steam turbine section

    SI. Parameters Unit Design TestNo.

    1 Load MW 210 208

    2 1SI stage steam pressure kg/cm 96.5 87

    3 Main steam temp before ESV 530 535

    4 Main steam enthalpy (h,) Kcal/kg 816.8 800.9

    5 Main steam flow (m,) T/hr 652.132 670

    6 FW temp before ECO (T2) C 244.65 247

    7 FW inlet enthalpy before ECO (h,) Kcal/kg 253.32 255.7

    8 Extraction steam pr-hph-7 (P7) kq/crn" 42.32 41.0

    9 Extraction steam temp-hph-7 (T7) C 386 416

    10 Extraction steam enthalpy-hph-7 (h.) Kcal/kg 760 778.32

    11 FW inlet temp to-hph-7 (Tg) C 222.6 223

    12 FW inlet enthalpy to hph-7 (hg) Kcal/kg 229.32 228.32

    13 FW temp outlet from hph-7 (T,o) C 243.62 246

    14 FW outlet enthalpy from-hph-7 (hlO) Kcal/kg 256.25 249.65

    15 Drip temp-hph-7 (T.) C 232.7 248

    16 Drip enthalpy-hph-7 (he) Kcal/kg 243.61 261.8

    17 FW flow (m,) T/hr 645.234 83

    18 Extraction steam pr-hph-6 (p.) kq/crn" 28.05 25.6

    19 Extraction steam temp-hph-6 (T.) C 315.6 348

    20 Extraction steam enthalpy-hph-6 (h.) Kcal/kg 729.57 748.07

    21 FW inlet temp to hph-6 (T3) C 190.12 184.23

    22 FW inlet enthalpy to hph-6 (h3) Kcal/kg 190.23 187.23

    23 FW outlet temp from-hph-6 (T4) C 222 223

    24 FW outlet enthalpy from-hph-6 (h4) KcaJ/kg 228.2 227.42

    25 Drip temp -hph-6 (Ts) C 204 228

    26 Drip enthalpy-hph-6 (hs) Kcai/kg 205.5 235.08

    27 IPT inlet steam pr(P'2) kq/cm" 28.31 24

    28 IPT inlet temp (T'2) C 530 535

    29 IPT steam inlet enthalpy (h'2) Kcal/kg 844.67 848.34

    30 HPT exhaust steam pr (P,,) kg/cm2 28.07 25

    31 HPT exhaust steam temp (T" ) C 320 332

    32 HPT exhaust steam enthalpy (h,,) Kcal/kg 729.29 737.73

    33 RH spray water flow (m'3) T/hr 0 26

    34 RH spray water enthalpy (h,,) Kcal/kg 253.13 255.58

  • h6, m6

    FWH6h4 h3m3

    h5

    Fig. 1heat balance diagram of feed water heater 6

    h10

    h8

    FWH7h9m12

    Fig. 2 heat balance diagram of feed water heater 7

    Fig 2 shows the heat balance diagram of feed water heater 7.This analysis is done in order to calculate the mass flow rateof steam coming from extraction 7.

    Bled steam flow, rn, =

    Bled steam flow, rn, =

    Reheat stream flow, m3= m,-(m6+m7)

    Heat flow from (h h)m3 '2 - 11

    reheater to turbine, Q2 = --3.6

    Heat flow fromreheater to spray water, Q3 =

    m'3 (h'2 - h,)3.6

    Total heat flow to turbine, Q = Q,+Q2+Q3

    Autumn 2010

    2. Energy and monetary savings estimation

    The improvement in turbine performance

    parameters and the savings are as shown

    below:

    Turbine heat rate (design) = 8639.48 kJ/k Whr

    Turbine heat rate (actual) = 8970.99 kJ/k Whr

    % difference in heat rate of turbine = 3.69

    HP cylinder efficiency = 80 %

    % Change in HPT cylinder efficiency = 8.1%

    = 0.146%

    Reduction in heat rate = 12.90 kJ/kWhr

    Saving in energy = 21.766 X 109kJ/year

    Assuming, the plant

    availability factor = 94.09 %

    Saving in coal

    consumption = 12.25 X 105 kg /

    year

    =4250 kcal/kg

    = Rs/year 3.062 x 106

    = 2500 Rs /tonnes

    Assuming, coal CV

    Monetary saving

    Assuming, coal cost

    3. Suggestions for energy conservation

    The following is the description for finding

    the potential of energy conservation in turbine

    section of 210 MW unit of a coal fired thermal

    power plant:

    Replacement of HP and LP turbine modulesalong with internals

    Existing 210 MW steam turbine (LMW design) is

    fitted with impulse blading. In this design, steam

    pressure drop takes place only in guide blades

    provided in the diaphragms. While passing

    through moving blades, there is negligible

    pressure drop. The purpose of the proposed

    modernization of HP and LP turbines (LMW

    design) is to provide a cost effective modification

  • ETJOURNALOFENGINEERING&TECHNOLOGY

    and upgradation package, to maximize the

    improvement in HP and LP turbine performance.

    The upgradation of HP and LP turbine is possible

    by incorporating the use of improved blade profile

    which results into reduction in the aerodynamic

    flow losses egoprofile loss, secondary flow loss and

    tip leakage loss. After renovation and

    modernization of HP and LP turbine by

    implementation of the proposal, their life is

    expected to be about 25-30 years. Design cylinder

    efficiency shall be as under:

    HP LP

    Old 80% 78%

    New 86.5% 80%

    The following are the benefits of improved bladeprofile:

    A) The improved design and cylinder efficiency

    shall help in reducing heat rate.

    B) The existing turbine requires large

    replacements as per RLA studies and should

    have run for more than 1, 50,000 hrs.

    C) Life extension

    Every type of energy optimization is about

    reducing the total cost of a generation, i.e.

    reducing the losses in relation to the cost,

    either by increasing the thermal efficiency of

    the process or the efficiency of its components.

    For example, a gain in the isentropic turbine

    efficiency is of high interest in the field of steam

    turbine research. Various losses related to

    blade profiles are:

    (I) Profile loss is usually referred to as the loss

    generated in the blade boundary layers,

    including the loss arising at the trailing edge

    [1].

    (ii) End-wall loss arises from the annulus

    boundary layers, and is sometimes referred to

    Autumn 2010

    as secondary flow loss to include all the

    losses that otherwise are not accounted for

    [4].

    (iii) Tip leakage loss arises from the leakage flow

    over the tips of rotors and the hub clearance

    between blade rows and the cavity flow. For

    upstream stages, the secondary flow loss

    and tip leakage loss also become important,

    and for admission stages in small-scale

    machines even more significant than the

    profile loss [5].

    RESULT

    The results of the present study are shown in

    Table 2. In this table, reduction in heat rate,

    saving in energy, saving in coal consumption

    and its equivalent monetary savings are shown.

    Table 2 Changes in percentage heat rate of turbineand savings with use of improved blade profile

    1. % change in heat rate 0.146%

    2. Reduction in heat rate 12.90kJ/kWhr

    3. Saving in energy 21.766 X 109kJ/year

    4. Saving in coal 12.25X 105consumption kg/year

    5. Monetary saving Rs/ year3.062 X 106

    CONCLUSION

    It can be analyzed that there are significant

    changes in percentage heat rate of turbine and

    savings from upgradation of HP turbine by use of

    improved blade profile. By upgradation of the

    HPT the estimated saving of energy is

    approximately 21.766 X 109 kJ/year and its

    equivalent monetary worth is nearly Rs. 30 lakhs. ''''"1I"T"""c::-::l

    00

  • REFERENCES:1. Melvin H. Chiogioji, Industrial Energy Conservation,

    Marcel Dekker, Inc. NewYork. Basel (1979); 19-31.

    2. http://www. iea. org/textbase/papers/2003/Coalfired fossilfuels.pdf

    3. http://w\vw.energy.qld.gov.au/i mag es/energy_balance.gif

    4. Gill C ENG A. B., MI Mech. E, Power PlantPerformance, 1st ed., Butterworth. Lund Boston

    Autumn 2010

    Durban, Singapore, Sydney, Toronto, Wellington,1984; 495-535.

    5. Hunt G. F.,Modem Power Station Practice, VolumeC, British Electricity International London,Pergamon Press, Oxford, New York, Seoul, Tokyo,1991; 2-13.

    6. Arthur P.Fraas, M. Necati Ozisik, Heat ExchangerDesign, John Wily & Sons, Inc. N York, London,Sydney, 1965; 241-255.

    000


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